docs: def sample(self, size=1):
          """ Sample rigid transform random variables.
  
          Parameters
          ----------
          size : int
              number of sample to take
          
          Returns
          -------
          :obj:`list` of :obj:`RigidTransform`
              sampled rigid transformations
          """
          samples = []
          for i in range(size):
              # sample random pose
              xi = self._r_xi_rv.rvs(size=1)
              S_xi = skew(xi)
              R_sample = scipy.linalg.expm(S_xi)
              t_sample = self._t_rv.rvs(size=1)
              samples.append(RigidTransform(rotation=R_sample,
                                            translation=t_sample,
                                            from_frame=self._from_frame,
                                            to_frame=self._to_frame))
  
          # not a list if only 1 sample
          if size == 1 and len(samples) > 0:
              return samples[0]
          return samples